US2165208A - Fluid heat exchange apparatus - Google Patents

Description

July 11, 1939. E. s. BAILEY FLUID HEAT- EXCHANGE APPARATUS Filed May 15. 1957 m Mb W m B G .H w r. E

ATTORNEY.

Patented July 11, 1939 UNETED STATES PATENT OFFECE FLUID HEAT EXCHANGE APPARATUS Application May 15,

7 Claims.

My invention relates to fluid heat exchange devices and it is concerned with improvements in the operative results obtained by such apparatus.

An object of my invention is to provide such marked increases in capacity of fluid heat exchange devices including a deep bank of convection heated tubes that economies of high degree are effected in the cost of power generation. The application of the invention results in a considerable increase in the operative life of the apparatus and minimizes outage, or the time during which the apparatus must be taken out of service for the purposes of repair.

The invention is exemplified as applied to that such tubes before they contact with a larger number of spaced water tubes connected into the boiler circulation. All of these water tubes may be arranged in groups which are referred to as tube banks. In such a boiler the foremost water tubes extending across the furnace exit are more intensely heated than the remaining tubes, and this is true even when the furnace walls include water tubes connected into the boiler circulation. This high degree of heating is due, in part, to the fact that direct furnace radiation is received by these tubes on their parts which are not shielded from the furnace. In addition, these foremost tubes are swept at high velocity by furnace gases which are at temperatures higher than those of the gases contacting the remaining boiler tubes. Thus, the foremost tubes are heated at heat exchange rates which are materially higher than the rates pertaining to the remaining boiler tubes, and the sum of the radiant and convection heat, per square foot of tube surface is considerably higher than elsewhere in the boiler.

Such high rates of heat absorption typical of the foremost Water tubes across the furnace exit, exposed to radiation from the furnace and also swept by the hottest furnace gases frequently result in the overheating of these tubes when the boiler is operated at high capacity. Furthermore, such overheating is intensified if the interior tube surfaces are fouled by accumulated sediment or scale because the thermal resistance of such internal deposits increases the metal temperatures when heat is flowing inward. To protect the tube metal in such cases of overheating when previ ously the clean tubes operated at lower and safe 1937, Serial No. 142,739

temperatures, it has been necessary to operate boilers at reduced capacity, and, in a given plant, it may consequently become necessary to install additional boilers.

Even when the internal surfaces of the water tubesare clean there is a certain capacity for a given rate of fuel combustion in the furnace high enough to cause overheating of the tubes across the furnace exit when there is no such overheating of the remaining water tubes. Thus an undesirably low capacity limit is imposed, and this limit is determined by conditions under which the foremost tubes will not be overheated- This limit is imposed in spite of the fact that the remainder of the water tube heating surfaces could safely make more steam if the limitwere exceeded. Consequently, a very small fraction of the total heating surface of the boiler limits the steam generating capacity of the entire boiler. My invention aims to remove such limitations and v to make it possible to increase the capacities of water tube boilers without danger of overheating the tubes across the furnace exit. I thus reduce the cost and weight of boilers, per unit of hourly steaming capacity, or per horsepower of the prime mover supplied by the boiler.

I accomplish the above indicated results by reducing the heat absorbing capacity of the water tubes extending across the furnace gas exit Without obstructing the flow of gases from the furnace. By reducing the heat absorbing capacity of these tubes I make it possible to burn greater quantities of fuel in the furnace and to generate a greater volume and weight of furnace gases. By avoiding obstructionsto the flow of this increased quantity of furnace gases past the furnace outlet tubes, I make that increased amount of gases available for generating steam in the remaining tubes of the boiler. Thus, the boiler capacity is increased without overheating a small part of the total heating surface which has previously limited boiler capacity.

My invention will be described with reference to embodiments thereof which indicate good examples of the application of the invention to steam boilers. However, the specific embodiments of the invention shown and described are not to be considered as limiting the invention. Contrariwise, the invention is to be taken. as applicable to other apparatus, within the scope of the subjoined claims.

I will now describe the illustrative embodiments of my invention shown in the accompanying drawing, in which Fig. 1 is a somewhat diagrammatic view in the erating tubes.

nature of a vertical'section of a steam boiler of the bent-tube type to which my invention is applied.

Fig. 2 is a transverse section across the front tube bank, taken on the line 22 of Fig. 1.

Fig. 3 is a transverse section of another embodiment of my invention applied to a boiler similar to that indicated in Fig. 1.

Fig. 4 is a detail transverse section through one of the water tubes of the Fig. 3 embodiment extending across the furnace gas exit.

Fig. 5 isan elevation of the water tube indicated in Fig. 4. I

. Fig. 6 is a transverse section of a different embodiment of the construction indicated in Fig. 4,

and

Fig. 7 is a side elevation of the construction indicated in Fig. 6.

One type of fluid heat exchange apparatus coming within the scope of myinvention, is a steam boiler such as that illustrated in Fig. 1 of the drawing. This boiler includes convection heated bands l0, l2, and M of spaced steam gen- As shown, these banks of tubes establish communication between a submerged drum l6, the steam offtake drum I8, the middle drum 2!], and the front drum 22. The latter three drums are connected by rows of steam circulators 24, 26,.and 28, and feed water may be supplied to drum 18 by any suitable connections.

Although the boiler shown in Fig. 1 has three gaspasses separated by the baflies 30 and32, my invention is applicable to different types of boilers, some of which may be single pass boilers. It is contemplated, for instance, that the invention shall be particularly applicable to boilers which do not have separated banks of tubes but, on the contrary, are provided with a single bank of tubes.

The steam generating tubes of the front bank I4 extend over a furnace 34 firedat high temper atures by combination fuel burners 36. These burners are adapted for burning gas and oil fuels,

but it is to be understood that the invention is not limited thereto. The burners might be capable of operation with other fuels suchas pulverized coal. The essential consideration is that the furnace be fired at high temperatures. This promotes the best combustion conditions and enables me to attain a high degree of economy of fuel consumption and alsoto-materially reduce the space requirements of boiler furnaces. v The front tubes/38 of the bank M are preferably arranged at their ends in single row formation with the tubes 40 but throughout their main portions extending over the furnace 34, these two sets of tubes are arranged in staggered formation so as to form a boiler slag screen. The arrangement of these tubes is clearly disclosed in Fig. 2 of the drawing.

The main parts of the tubes 38 may be described as extending across the gas exit of the furnace 34, but at any rate, they are nearest the furnace 34 so that they arenot only heated by direct furnace radiation, but are swept at high velocity by the furnace gases at temperatures higher than the temperatures of the gases contacting with the remaining tubes of the boiler. The maximum temperatures which such tubes when bare can safely stand impose a relatively low capacity limit upon the boiler when the tubes are provided as above, described, but this limit is removed by' the embodiments of my invention indicated from 2-7, inclusive.

In Fig. 2 the high temperature tubes 38 are provided with metallic studs 42, preferably Welded to the tubes at distributed positions over the sides of the tubes facing the furnace. Around the studs and over the furnace faces of the tubes 38 high temperature refractory material 44 is installed in a plastic or semi-plastic condition. This material is highly refractory, and it sets un der the action of heat absorbed from the furnace into a hard rigid material. vWhile in a plastic or semi-plastic condition it is molded about the studs and the outer portions of the tubes and is compacted in the spaces between the tubes and the studs by tamping or hammering, to eliminate voids and to insure close contact between it and the studs and tubes. The semi-plastic material preferably takes somewhat of an air set, and itis subsequently sinteredand bonded to the studs by reason of the reactions caused by the high fur-' nace temperatures. Due to partial fusion of the outer ends of the studs 42, and to other causes including chemical reactions, the studs and the tube metal become mechanically and chemically bonded with the refractory material so that good heat transfer relationship is maintained therebetween. This enables the cooling effect of the fluid in the tubes 38 to be effective, upon the refractory material through the metal of the studs, so that a balance is set up between the tendency of the high temperature furnace gases to fuse away the ends of the studs and outer face of the refractory material, and the resistance of thecomposite tube construction to such action,

With reference to the Fig. 2 construction, it will be noted that the widths of the gas passes between a tube 40 and adjacent tubes 38 are at least equal to or greater than the width of the gas passes between adjacent tubes of the rows 48 and 50 even when the tubes 38 are covered by the refractory material as above set forth. Therefore the construction of this invention as indicated in this figure offers no greater obstruction to gas flow than a bank of tubes in which all of the tubes are uniformly arranged with the spacing of the tubes in the rows 48 and 50.

In the embodiment of my invention indicated in Fig. 3, the tubes in'each of the rows 54, 56, and 58 have the same spacing. The refractory structures carried by the tubes of the row 58 donot extend into the gas passages'between successive tubes in the rows. In other words, these refractory structures have the same, or less width than the tubes of the row 58. This is another arrange ment of elements in which the application of my invention increases the boiler capacity without increasing the resistance of gas flow. 7

The refractory structures 60 are shown somewhat in detail in Figs. 4 and 5. In the latter, the studs 52. are formed so as to structurallyjbond the refractory material'M to the tube 66. For this purpose the studs are formed with their outer ends wider; or thicker, than their inner ends.

After the studs are welded to the tubes the refrac tory material 64 is installed as a plastic and allowed to take a set so that itwill be maintained on the tube.

In the species of the invention indicated in Figs. 6 and 7 of the drawing, the studs are replaced by converging bars 68 extending longitudinally of the tubes and welded thereto, as indicated at T8. The refractory material 12 is installed as a plastic between the bars 68, and it is bonded thereto by reason of the converging relationship of the bars in addition to the chemical and mechanical bonding referred to above.

When the bars 68 are constructed with the spaced extensions 14, the development of undesirable stresses is minimized. Also, this particular construction facilitates manufacture inasmuch as two of the bars 68 may advantageously be cut from a single bar of greater width.

While the invention has been described with reference to the particular embodiment shown in the drawing and described in the specification, it is to be understood that the invention is not limited to all of the details thereof, but that it is rather of a scope commensurate with the scope of the subjoined claims.

I claim:

1. In a vapor generator including a bank of tubes having normal tube spacing and extending across the path of high temperature furnace gases, means decreasing the heat absorption capacity of the front tubes of said bank first contacted by the furnace gases and increasing the capacity of the generator while maintaining the maximum gas flow area between said front tubes, said means consisting of refractory structures in good heat exchange relationship with the metal of said front tubes over their furnace faces and being so arranged with the front tubes that the normal gas passages between the tubes of the bank are not decreased in width.

2. In a water tube steam boiler, a bank of spaced and inclined tubes extending across the path of high temperature furnace gases, the tubes being in one group and so arranged that the gases pass across them in one direction, means connected to the tubes to provide for the entry of water into the lower ends of the tubes and the discharge of water or a mixture of steam and water from the upper ends of the tubes, and heat resistant means in good heat exchange relationship with the front row tubes of said bank presenting faces toward the oncoming furnace gases and operating to increase the capacity of the boiler while maintaining the maximum gas flow area between said front row tubes.

3. In a steam boiler, a bank of steam generating tubes extending across the path of high temperature furnace gases, the tubes being in one group and so arranged that the gases pass across them in one direction, means connecting the tubes into the boiler circulation, and heat resisting structures extending only over the faces of the front tubes of said bank presented toward the oncoming furnace gases, said structures operating to increase the capacity of the boiler without obstructing the normal gas passage between said tubes.

4. In a water tube steam boiler having a deep bank of inclined steam generating tubes having normal tube spacing and extending across the path of high temperature furnace gases, means increasing the steam generating capacity of the boiler, said means consisting of refractory structures in good heat exchange relationship with the metal of the front tubes first heated by the oncoming furnace gases, said structures and front tubes being so arranged that the maximum gas flow areas between adjacent front tubes are maintained.

5. In a vapor generator including a bank of tubes extending across the path of high temperature furnace gases, the tubes being in one group and so arranged that the gases pass across them in one direction, means for increasing the capacity of the generator by limiting the heat absorption capacity of the front tubes of said bank while maintaining the maximum gas flow area between adjacent front tubes in a row extending transversely of gas flow, said means consisting of refractory structures in good heat exchange relationship with the metal of said front tubes over the furnace faces of the latter.

6. In fluid heat exchange apparatus having a bank of spaced tubes extending across the path of high temperature furnace gases, the tubes being in one group and so arranged that the gases pass across them in one direction, means increasing the capacity of the apparatus while maintaining the maximum flow areas between adjacent front tubes of said bank in a row transversely of gas flow, said means consisting of refractory structures in good heat exchange relationship with the metal of the said front tubes, the refractory means of each of said front tubes being of a width not greater than the outside diameter of the associated tube.

'7. In a vapor generator including a bank of tubes extending across the path of high temperature furnace gases, a furnace across the exit of which said tubes are positioned, means burning a non-slagging fuel in the furnace, means for increasing the capacity of the generator by limiting the heat absorption capacity of the front tubes of said bank while maintaining the maximum gas flow area between adjacent front tubes in a row extending transversely of gas flow, said means consisting of refractory structures in good heat exchange relationship with the metal of said front tubes over the furnace faces of the latter.

ERVIN G. BAILEY.

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